Two important challenges leading to the ubiquitous use of wireless sensor nodes in body area networks (BAN) are small size and low power consumption. Radio power typically consumes the majority of the total power in a sensor node and therefore is a significant bottleneck in energy-efficient design. One technique used to reduce power consumption in a BAN is to use asynchronous communication that keeps the higher-power communication radio in a low-power sleep state. Radios, with power consumption as low as 50 μW, are a common technique used to achieve this. However, they are on at all times, and therefore contribute significantly to the total energy consumption of the node. Further power reduction is needed to improve sensor node lifetime to the point where it can be used without interruption in a BAN.
FIG. 1 shows a power vs. sensitivity comparison survey of published ultra-low power radios (top left) and energy harvesters (lower right) from 2005-2012. The plot is divided into two sections: 1) low-power radios that consume power, and 2) energy-harvesters that generate power.
Looking at the low power radio section, an empirical slope of −½ is apparent for radios with a sensitivity less than −60 dBm. This slope is influenced by several parameters, such as the variation in data rate, architecture, need for amplification at RF frequencies, and non-linearity present in the radios. The survey only covers ultra-low power receivers, common in BAN research; therefore, Bluetooth or Zigbee receivers with higher power will sit well above this line. A noticeable power floor around 50 μW is present, caused by a minimum power requirement for achieving gain at RF.
In the energy-harvester section, an empirical slope of −½ is also apparent in the data for sensitivity higher than −30 dBm. Below −30 dBm, received voltages are not sufficient to fully commutate the rectifier stages, and power-harvesting efficiency drops sharply.
When plotted together in FIG. 1, one can see a region below 50 μW and between −60 dBm to −36 dBm where communication does not exist. Obviously to the left and above this region radios have been demonstrated and to the right the received power is high enough that rectification could be used to communicate with zero power. The goal of this work is to explore this region, near the intersection of the extrapolated trend lines by targeting a radio with a sensitivity of −40 dBm and power consumption <1 μW.
Therefore, this disclosure presents a low power radio with an active area to address both of the challenges above while operating near the intersection of the extrapolated trend lines in FIG. 1. This section provides background information related to the present disclosure which is not necessarily prior art.